(1) Field of the Invention
The invention relates to a method of metallization in the fabrication of integrated circuits, and more particularly, to a method of avoiding contamination in copper metallization in the manufacture of integrated circuits.
(2) Description of the Prior Art
Copper metallization has become a future trend in integrated circuit manufacturing. However, copper contamination of the intermetal dielectric layer is a problem. For example, as shown in FIG. 1, a first copper metallization 23 has been formed in a dielectric layer 18. An intermetal dielectric layer 25 is formed over the first copper metallization. When a via 27 or a dual damascene opening is made through the intermetal dielectric layer 25 to the underlying first copper metallization 23, some of the underlying copper will be sputtered away and redeposit 29 onto the sidewall of the via or dual damascene opening. This will cause contamination of the intermetal dielectric layer. This contamination may lead to line-to-line shorts and will degrade device performance. It is desired to prevent copper contamination of the intermetal dielectric layer.
U.S. Pat. No. 5,451,551 to Krishnan et al teaches a method of forming a titanium tungsten cap over copper and polishing away the excess capping layer. U.S. Pat. No. 5,470,789 to Misawa shows a titanium nitride layer that is buff-abraded. These two patents teach a similar capping layer to that in the present invention. However, since the step height between the open area and the copper recess is not large, the CMP (or buff abrasion) removal selectivity between the open area and the recessed area will also be small. As over-polishing is needed to remove the conductive capping layer between trenches, it is very likely that all of the conductive cap material on some of the trenches will be removed during over-polishing. U.S. Pat. No. 5,693,563 to Teong shows a barrier layer for copper, but the copper metallization is not recessed. U.S. Pat. No. 5,744,376 to Chan et al discloses a capping layer over a non-recessed copper metallization. U.S. Pat. No. 5,731,245 to Joshi et al teaches a hard cap for a tungsten plug process. U.S. Pat. No. 5,814,557 to Venkatraman et al forms a capping layer over a non-recessed copper layer.